... people have replaced the drive shaft flex disk - guibo - without removing the exhaust... My experience with exhausts is that something always breaks and takes ages to fix - so would like to avoid removing it.

Apparently that depends on this:

... the drive shaft slid on it's spline. Some will not side back far enough and require the center support to be removed which requires the exhaust to be removed.

And the word is supposed to be giubo, pronounced jew-bow.
"Giubo is a contraction of the Italian word giunto ('joint' or 'coupling') and the surname of the Italian engineer who designed and patented the first flex disc, Antonio Boschi (b1896-d1988). He later founded GIUBO SpA, a company solely dedicated to manufacturing flex discs."
https://en.wikipedia.org/wiki/Giubo

 

The drive shaft has a slip joint so it can lengthen and shorten with temperature, suspension motion, etc. You need to move it about half an inch to get the disk out or in.
Also note the arrows on the side of the giubo. They must point toward the flange. Also, the nuts are one-time use, so they need to be replaced, but you might as well replace the bolts while you're there.

 

Some might consider it sacrilege but... The heat shield is fairly pliable and can be cut and bent as required and folded back into place with less effort and risk than a what rusted up exhaust has. I have my reservations about having any dead weight hanging against rusted flange attachments anyway. So I'm snipping the shield right up the middle and folding it away like I'm doing surgery. If it works I'll just fold it back up put the screws in and maybe some aluminum foil tape or glue too.